Electromagnetic Environment Quiz

Electromagnetic Environment (5.14) Learning Objectives

• Understand how to minimize or prevent EMI/RFI from being generated by devices
• Explain the influence of EMC (electromagnetic compatibility) on maintenance practices for electronic systems (Level 2)
• Explain the influence of EMI (electromagnetic interference) on maintenance practices for electronic systems (Level 2)
• Explain the influence of HIRF (high intensity radiated field) on maintenance practices for electronic systems (Level 2)
• Describe the influence of lightning and lightning protection on maintenance practices for electronic systems (Level 2)

Electromagnetic Interference in Electrical Systems

• Electromagnetic Environment Terminology

  • Electromagnetic Environment (EME): The totality of electromagnetic phenomena at a given location
  • Electromagnetic Compatibility (EMC): Equipment ability to operate effectively in the intended operational electromagnetic environment
  • Electromagnetic Interference (EMI): Any electromagnetic disturbance disrupting or limiting electronic equipment
  • High-Intensity Radiated Field (HIRF): Man-made sources of electromagnetic radiation external to an aircraft
  • Radio Frequency Interference (RFI): Electromagnetic interference in the radio frequency spectrum

• Avionic Frequency Bands

  • VHF Omnidirectional Range (VOR): Radio beacon for point-to-point navigation (108-118 MHz)
  • Glideslope Systems: Used during landings (328-335 MHz)
  • Distance-Measuring Equipment (DME): Gauges aircraft-to-ground distance (over 1 GHz)
  • Global Positioning, Collision Avoidance, and Cockpit Weather Radar: Systems using frequencies above 1 GHz

PED Frequency Bands

• Personal Electronic Devices (PEDs) operate at frequencies from 10 kHz to 400 MHz.
• Emitted frequencies cover almost the entire range of navigation and communication frequencies on aircraft
• The entire system of electronic equipment aboard aircraft is at risk of EMI

EMI Permeation

• Inadequate shielding, damaged shielding, or degraded shielding due to corrosion
• Shielding effectiveness relies on good grounding.
• Wires can pick up interfering signals directly.
• Aircraft antennas outside the plane's skin can pick up EMI radiated through passenger windows and other unshielded openings
• RFI from a passenger device can enter a navigation receiver, autopilot computer, or other avionics device

Electromagnetic Interference

• In the 1980s, electromagnetic interference disrupted an aircraft's electronic controls
• EMI interruption of electronic or electrical equipment effectiveness
• Aircraft designed and built to withstand various electromagnetic fields
• EMI can jam sensitive equipment, damage electric circuits, and disrupt or shutdown critical avionics systems

Electromagnetic Compatibility

• EMC is the equipment's ability to operate satisfactorily in its electromagnetic environment without disturbing other electrical devices

Elements of an EMC Problem

• Source of electromagnetic phenomenon
• Receptor (target) that cannot function due to the phenomenon
• Path allowing the source to interfere with receptor
• EMC problems solved by identifying and mitigating two of these elements

Coupling Path

• Conducted, inductively coupled, capacitively coupled, and radiated coupling methods

Electric and Magnetic Fields

• Electric fields have one pole, magnetic fields have two
• Lines of electric force travel in straight lines outward from the center of the origin
• Electric fields are created by voltages, magnetic fields by currents

Leakage and Antenna Effect of Conductors

• Daily life frequencies range from AC power to mobile phone frequencies
• Mains rectifiers create switching noise
• Thyristor-based DC motor drives and phase-angle AC power control are sources of emissions

Emissions from a 70 kHz Switching Power Supply

• Digital technology can interfere with a broad frequency spectrum

High-Intensity Radiated Field (HIRF)

• HIRF is man-made electromagnetic radiation external to aircraft
• Caused by devices, such as radar, broadcast systems, and missile systems
• Frequencies above 400 MHz often narrow-beamed or pulsed
• Modern warfare systems contribute to high-frequency signals

EMI Management

• Determine the mechanism for energy transfer (radiation, conduction, or induction)
• Options for radiated EMI: Remove the source, harden the target (recipient), or separate the device
• Effective shielding anticipates radiated susceptibility and radiated emissions
• Multi-shielding improves attenuation across frequencies

EMI Minimization

• Using twisted wires: Balancing/earthing current in connection wires to prevent interference
• PCB continuous ground plane: Prevents EMI by absorbing and channeling electromagnetic energy

Structure Shielding

• Metal structures (like fuselages) block electromagnetic fields entering.
• This is based on total charge contained within enclosed conductive surface being zero.